Key results: cos(20)*cos(40)*cos(80) = 1/8. sin(20)sin(40)sin(80) = sqrt$\frac{3}{8}$. These use the technique of multiplying by 2sin(theta) repeatedly and applying double angle formulas. General: product of cos(theta)cos(2theta)...*cos(2^(n-1)*theta) = sin$\frac{2^n*theta}{(2^n*sin(theta)}$).